One of the best ways to improve the sound of your bass guitar is to upgrade your pickups. The pickups capture vibrations made from the notes you play and turn them into electrical signals, allowing amplification. Changing out the pickups on your bass can give you a cleaner tone and a more professional sound.
Unwind the tuning pegs on the headstock of your bass and remove the strings. The headstock of your bass guitar is the top piece above the fretboard where the strings enter the tuning pegs; the tuning pegs are the little pieces that stick out from the headstock, which are used to tune the strings.
Use a screwdriver to remove the pickguard, the piece of plastic that covers the body of your guitar and keeps it from getting scratched by the pick when you play, and get access to the electronics of the guitar. The volume knobs, selector switch and pickups all fit inside the guard.
Use the soldering iron to unsolder the electrical wires from the pickups. Unscrew the pickups from the body of the bass guitar.
Strip the wires from the new pickups and solder them to their proper locations. Make sure your soldering iron is hot.
Screw the new pickups in the body of the bass guitar. Allow the soldering work to cool, then stuff the pickup wires into the body.
Replace the pickguard and restring your bass guitar. Plug your bass guitar into your amplifier and test for any buzzing or humming. If there is any, check for faulty wiring.